<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn">我是学渣</button>
    <script type="text/javascript">
    var btn = document.getElementById('btn')
    btn.addEventListener('click',fn2);
    btn.addEventListener('dblclick',fn1);
    var num = 0;
    //老师，额，后面的我不会写了，您信吗
</script>
</body>
</html>